Preparation method of freeze-dried goat yoghurt powder rich in lactic acid bacteria

Abstract

The invention provides a preparation method of freeze-dried sour goat milk powder rich in lactic acid bacteria. The preparation method sequentially comprises the following steps: dissolving, inoculating and fermenting, seasoning and premixing, homogenizing, freeze-drying and the like. Alpha-cyclodextrine is added before fermentation to embed goaty-flavor substances, and fermentation and multi-stage freeze-drying processes are optimized, so that the survival rate of lactic acid bacteria and the retention rate of nutritional ingredients are remarkably increased. The viable count in the obtained product is not less than 3.0 * 10 < 7 > CFU / g, the shelf life exceeds 12 months, the taste is good, the flavor is obviously improved, and the product is suitable for nutritional supplement and intestinal health regulation of people of multiple age groups. The method is simple and convenient to operate and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of dairy processing technology, and in particular to a method for preparing freeze-dried yogurt powder rich in active lactic acid bacteria, with optimized flavor and suitable for room temperature storage. Background Technology

[0002] Goat milk, with its small fat globules, soft protein curds, rich content of medium- and short-chain fatty acids, and primarily containing A2-type β-casein, offers significant advantages in promoting digestion and absorption while reducing the risk of allergies. It is suitable for people with lactose intolerance and the elderly, as well as those with weaker digestive systems. Yogurt, on the other hand, undergoes fermentation where lactic acid bacteria partially break down lactose and protein, improving not only its taste but also its nutrient absorption rate and probiotic properties. It also effectively regulates gut microbiota and boosts immunity.

[0003] However, liquid yogurt suffers from problems such as decreased lactic acid bacteria activity and a short shelf life during storage and transportation, limiting its widespread application. To extend shelf life and facilitate carrying and use, the industry has gradually developed a technology for drying yogurt. Traditional processes often employ spray drying, which is highly efficient and low-cost, and is widely used in milk powder production. However, this method has significant drawbacks: First, the high temperatures required during spray drying can easily damage heat-sensitive nutrients, especially B vitamins and vitamin C, which are easily degraded under high temperatures, leading to a reduction in the nutritional value of the product. Secondly, active lactic acid bacteria are extremely sensitive to high temperatures and are largely inactivated during the spray drying process. As a result, the number of lactic acid bacteria in the final product is much lower than that in the fermented raw milk, which affects its core health functions such as intestinal regulation and immune enhancement. Furthermore, some flavor issues are difficult to control. Medium- and short-chain fatty acids in goat milk, such as caproic acid and caprylic acid, can cause a strong goaty odor, affecting consumer acceptance. Current methods lack effective means to suppress these unpleasant odors.

[0004] Freeze-drying, as a vacuum low-temperature dehydration technology, has significant advantages in dairy processing. It can achieve sublimation drying of aqueous substances at relatively low temperatures, better preserving the structure and function of heat-sensitive active substances, and is widely used in the preparation of high-end dairy products. It is particularly suitable for preserving active probiotics, helping to improve the survival rate of lactic acid bacteria in finished products and extend product shelf life.

[0005] Furthermore, α-cyclodextrin, due to its hydrophobic cavity structure, can form stable inclusion complexes with the odor-causing substances in goat milk, thereby masking off-flavors and improving flavor. Without interfering with the growth of lactic acid bacteria, it enhances the sensory appeal of the product by forming non-covalent complexes with target molecules.

[0006] Most current methods for preparing fermented goat milk powder fail to simultaneously preserve live bacteria, maintain nutrients, and control flavor, resulting in problems such as low lactic acid bacteria survival rates, poor flavor, and loss of heat-sensitive nutrients. Therefore, there is an urgent need for a feasible, highly active, sensory-enhancing, and long-shelf-life freeze-dried yogurt powder preparation method to overcome existing technological bottlenecks and promote the quality improvement and industrial application of related products. Summary of the Invention

[0007] To overcome the technical problems of low lactic acid bacteria survival rate, significant loss of heat-sensitive nutrients, poor flavor acceptance, and short shelf life in existing yogurt goat milk products, this invention provides a freeze-dried yogurt goat milk powder rich in lactic acid bacteria and its preparation method. This method achieves a balance between efficient preservation of live bacteria, flavor improvement, and product stability by optimizing the fermentation system, introducing flavor masking technology, and combining a multi-stage freeze-drying process. The technical solution of this invention is described in detail below with reference to several possible implementation methods: In one embodiment of the present invention, a method for preparing freeze-dried lactic acid goat milk powder rich in lactic acid bacteria is provided, comprising the following steps: S1. Dissolving: Mix whole goat milk powder with sterile water at 40℃ to 50℃ to dissolve it and obtain goat milk liquid; S2. Inoculation with starter culture: Add yogurt starter culture and α-cyclodextrin to the sheep milk and mix well; the yogurt starter culture contains lactobacillus and thermophilic streptococcus. S3. Fermentation: The inoculated sheep milk is fermented at a constant temperature of 41℃ to 43℃ for 6 to 8 hours, and then matured at 2℃ to 4℃ for 10 to 12 hours to obtain sour sheep milk. S4. Seasoning premix: Dissolve maltitol solution, isomaltulose and maltodextrin in sterile hot water and prepare a homogenate, then mix it evenly with the sour goat milk; S5. Homogenization: The mixture is homogenized at 40℃ to 45℃ and 20MPa to 25MPa pressure. S6. Freeze-drying: The homogenized material is subjected to quick-freezing, low-temperature freeze-drying, rewarm freeze-drying and room-temperature freeze-drying in sequence to obtain freeze-dried product, which is then crushed and packaged to obtain the freeze-dried yogurt powder. The freeze-drying step includes: (1) Quick-freezing: Quick-freeze at -50℃ for 4 to 6 hours; (2) Low-temperature freeze drying: freeze drying for 1 to 2 hours at -50℃ to -40℃ and vacuum degree ≤50Pa; (3) Re-temperature freeze drying: freeze-dry for 3 to 4 hours under conditions of -30℃ to 0℃ and vacuum degree ≤50Pa; (4) Freeze-drying at room temperature: freeze-dry for 10 to 12 hours at 10°C to 30°C and vacuum degree ≤50Pa.

[0008] Further, in step S1, the ratio of whole goat milk powder to sterile water is 100g to 120g of whole goat milk powder to 1L of sterile water.

[0009] Preferably, in step S2, based on the total amount of sheep milk, the amount of yogurt starter added is 0.08% to 0.1% (w / v), and the amount of α-cyclodextrin added is 0.1% to 0.3% (w / v).

[0010] Further, in step S4, based on 100 mL of the fermented goat milk, the amount of maltitol solution added is 6.0 g to 8.0 g, the amount of isomaltulose added is 6.0 g to 8.0 g, and the amount of maltodextrin added is 1.0 g to 2.0 g; the amount of sterile hot water used is 30 mL to 50 mL.

[0011] Preferably, in step S3, the temperature of the constant temperature fermentation is 41°C to 43°C, and the fermentation time is 6 hours to 8 hours; the temperature of the post-ripening is 2°C to 4°C, and the post-ripening time is 10 hours to 12 hours.

[0012] Preferably, in step S6, the quick-freezing time is 4 to 6 hours; the low-temperature freeze-drying temperature is -40°C to -50°C; the warm-up freeze-drying time is 3 to 4 hours; and the room temperature freeze-drying time is 10 to 12 hours.

[0013] Optionally, the yogurt starter may also include Bifidobacteria.

[0014] In one embodiment of the present invention, a freeze-dried yogurt powder prepared by the above-described method is provided, characterized in that the total number of active lactic acid bacteria in the freeze-dried yogurt powder is not less than 3.0 × 10⁻⁶. 7 CFU / g, which contains Streptococcus thermophilus and Lactobacillus.

[0015] Preferably, the viable count of the thermophilic streptococci is not less than 2.0 × 10⁻⁶. 7 CFU / g, the viable count of the lactobacillus is not less than 1.0 × 10⁻⁶. 7 CFU / g.

[0016] Optionally, the freeze-dried yogurt powder has a shelf life of more than 12 months at room temperature.

[0017] Based on the above technical solution, the method for preparing freeze-dried yogurt powder rich in lactic acid bacteria of the present invention significantly improves the survival rate of lactic acid bacteria, maximizes the preservation of heat-sensitive nutrients, significantly extends the shelf life of the product, and effectively improves the flavor of yogurt by constructing an optimized process flow including dissolution, inoculation and fermentation, flavoring and mixing, homogenization and multi-stage freeze drying.

[0018] In this invention, by adding 0.1% to 0.3% of α-cyclodextrin to sheep milk before fermentation, its hydrophobic internal structure selectively encapsulates short- and medium-chain fatty acids with a goaty odor (such as caproic acid, caprylic acid, etc.), which can effectively reduce the release of unpleasant flavors, improve the overall sensory acceptance of fermented goat milk, and at the same time, not affect the normal growth and fermentation process of lactic acid bacteria, thus ensuring the quality stability and repeatability of the product.

[0019] During the fermentation stage, a constant temperature environment of 41℃ to 43℃ is used to control fermentation for 6 to 8 hours, followed by 10 to 12 hours of maturation at 2℃ to 4℃. This allows the lactic acid bacteria to fully metabolize and produce acid, forming an ideal gel structure, thus improving the taste and the stability of the bacterial community. Subsequent seasoning addition steps utilize low-GI sweeteners such as maltitol and isomaltulose, creating a complex formula that combines improved taste with functional nutrition.

[0020] During the homogenization and freeze-drying stages, this invention employs a homogenization pressure of 20 MPa to 25 MPa and a temperature of 40°C to 45°C for refinement, which helps stabilize the suspension state of lactic acid bacteria and ensures uniform mixing. Subsequent multi-stage freeze-drying steps (including rapid freezing at -50°C, low-temperature freeze-drying at -40°C to -50°C, rewarm freeze-drying at -30°C to 0°C, and room-temperature freeze-drying at 10°C to 30°C) effectively prevent thermal inactivation and structural damage of the lactic acid bacteria by controlling the gradient increase in temperature and vacuum (≤50 Pa), while maximizing the retention of heat-sensitive nutrients such as protein, vitamin C, and B vitamins.

[0021] The final freeze-dried yogurt powder product has a total viable count of lactic acid bacteria of not less than 3.0 × 10⁻⁶. 7 CFU / g, which can reach 3.68 × 10⁻⁶ under certain preparation conditions. 7 With a CFU / g content, both Streptococcus thermophilus and Lactobacillus maintain high activity levels, and the product has a shelf life of over 12 months at room temperature, making it suitable for consumers with a significant demand for highly active probiotics.

[0022] In summary, this invention provides a freeze-dried yogurt powder preparation process that balances the preservation of active bacteria, flavor improvement, nutrient preservation, and storage stability, and has good industrial promotion value and market application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow for preparing a freeze-dried lactic acid goat milk powder rich in lactic acid bacteria according to the present invention. Detailed Implementation

[0024] To better understand the technical solution and beneficial effects of the present invention, the preparation method of the present invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments are for illustrative purposes only and are not intended to limit the present invention. Without departing from the core idea of ​​the present invention, those skilled in the art can make appropriate adjustments or changes to the specific conditions, proportions, and sequence of steps, and these equivalent modifications should also be covered within the protection scope of the present invention.

[0025] Example 1

[0026] In this embodiment, a method for preparing freeze-dried lactic acid goat milk powder rich in lactic acid bacteria is provided, and the specific process steps are as follows: Step 1: Dissolve Weigh 100g of whole goat milk powder and slowly add it to 1L of preheated 45℃ sterile water while stirring to ensure it dissolves completely and forms a homogeneous goat milk solution. To ensure sterility, the equipment can be sterilized using 121℃ high-pressure steam sterilization to prevent contamination by other microorganisms from affecting subsequent fermentation.

[0027] Step 2: Inoculate with fermenting agent When the goat milk is cooled to approximately 42°C, add 1.0g of yogurt starter containing active strains of Lactobacillus and Streptococcus thermophilus, along with 0.3% (w / v) α-cyclodextrin as a flavor masking agent. Mix thoroughly to ensure even distribution of the bacteria, forming the fermentation preparation solution. The addition of α-cyclodextrin effectively encapsulates the goaty fatty acids in goat milk without affecting the metabolic activity of lactic acid bacteria.

[0028] Step 3: Fermentation and Post-Ripe The inoculated mixture was placed in a constant temperature fermentation chamber and fermented continuously at 41℃ for 8 hours to allow the lactic acid bacteria to fully multiply, produce acid, and form a gel structure. After fermentation, the fermented goat milk was transferred to a 2℃ environment for 10 hours of post-fermentation maturation to promote flavor maturation and texture stability. The pH of the fermented product was controlled between 4.2 and 4.4, which meets the requirements for yogurt flavor.

[0029] Step 4: Premix the seasonings Weigh 6.0g of maltitol and 6.0g of isomaltulose, dissolve them thoroughly in 30mL of sterile hot water (approximately 60℃) to prepare a sweetened homogenate. While pouring the premixed solution into the yogurt, stir continuously to ensure even distribution of the sweetener and form a flavorful mixed yogurt base.

[0030] Step 5: Homogenize The above-mentioned mixed yogurt base material was placed in a homogenizer and homogenized once at a pressure of 25 MPa and a temperature of 45°C to form a stable dispersion system of milk fat and sweetener components in the material. This step helps to improve the smoothness of the texture and the uniformity of the subsequent freeze-drying structure.

[0031] Step Six: Freeze-drying First, place the homogenized liquid in a tray, spread it evenly, and then perform the following freeze-drying operations in sequence: Quick-freezing stage: The material is placed at -50℃ for 4 hours to form a solid structure; Low-temperature freeze-drying stage: Preliminary sublimation and dehydration are carried out for 1 hour at -40℃ and vacuum degree ≤50Pa; Re-freeze drying stage: Gradually raise the temperature to -30℃~0℃, control the vacuum degree at ≤50Pa, and continue freeze drying for 3 hours to remove deep moisture; Room temperature freeze-drying stage: The temperature is further increased to 10℃~30℃, and the vacuum degree is maintained at ≤50Pa. Freeze-dry for 10 hours to ensure that the moisture content is reduced to below 3% and obtain a stable and loose freeze-dried product.

[0032] Step 7: Crushing and Packaging After freeze-drying, the block-shaped freeze-dried material is removed, lightly crushed using a pulverizer, and sieved until it becomes a uniform fine powder. Immediately, it is packed into aluminum foil composite bags in a clean environment and sealed using vacuum or nitrogen-filled packaging to prevent air oxidation and moisture reabsorption, ultimately yielding a freeze-dried yogurt powder product rich in lactic acid bacteria.

[0033] Product testing and performance evaluation To evaluate the microbial activity and sensory quality of the freeze-dried yogurt powder prepared in this embodiment, total bacterial count and sensory evaluation tests were conducted.

[0034] 1. Detection of total number of live lactic acid bacteria colonies The thermophilic streptococci and lactobacilli in the lyophilized samples were counted using the dilution plating method. The results are shown in Table 1. Table 1. Statistical analysis of total bacterial count in freeze-dried yogurt goat milk powder

[0035] The test results show that the survival rate of lactic acid bacteria in the product treated by the method of this invention is significantly higher, and the total number of live bacteria is much higher than that of traditional spray-dried products, which can reach 10. 6 The CFU / g level meets the prebiotic performance requirements of functional dairy products.

[0036] 2. Sensory evaluation test To verify the effects of different additives on improving the flavor of yogurt, a comparative group was designed to evaluate color, aroma, taste, sweetness and sourness, and overall acceptability. A 9-point scale was used for scoring, and the results are shown in Table 2. Table 2 Sensory Evaluation Scores of Freeze-Dried Yogurt

[0037] The scoring results show that the group with 0.3% α-cyclodextrin was significantly better than the blank group and other groups in terms of aroma and taste. The average score of the comprehensive evaluation reached 6.77 points, indicating that the amount added can effectively mask the goaty smell of goat milk and improve the overall sensory quality, and does not interfere with the normal fermentation of lactic acid bacteria.

[0038] Example 2

[0039] In this embodiment, the same process flow as in Example 1 is used, but some key process parameters are adjusted to verify the adaptability of the present invention under different conditions and the consistency of the product. The specific steps are as follows: Step 1: Dissolve Weigh 100g of whole goat milk powder and add it to 1L of sterile water preheated to approximately 50°C. Mix thoroughly to ensure the milk powder is fully dissolved and forms a homogeneous goat milk solution. To enhance dissolving efficiency and reduce foaming, the surface of the milk powder can be pre-wetted before stirring to prevent clumping.

[0040] Step 2: Inoculate with fermenting agent After the temperature of the goat milk stabilizes at approximately 43°C, add 1.0g of yogurt starter culture. The starter culture consists of Bifidobacterium, Lactobacillus, and Streptococcus thermophilus, and the three active bacteria are mixed in a certain proportion to help enhance intestinal function regulation. Simultaneously, add 0.3% (w / v) α-cyclodextrin and gently stir to disperse it evenly, forming a fermentation mixture. This step is completed in a clean environment to prevent contamination of the fermentation system by other microorganisms.

[0041] Step 3: Fermentation and Post-Ripe The inoculated mixture was transferred to a sealed fermentation tank and fermented at a constant temperature of 43°C for 6 hours. This temperature is suitable for promoting rapid acid production by Streptococcus thermophilus and also conducive to the growth of Bifidobacteria. After fermentation, the mixture was quickly transferred to a 4°C refrigerated environment for 12 hours of post-fermentation to further enhance the flavor, richness, and stability of the yogurt.

[0042] Step 4: Premix the seasonings Weigh out 8.0g maltitol, 8.0g isomaltulose, and 2.0g maltodextrin, and add them to 50mL of sterile hot water at approximately 60℃. Stir rapidly until completely dissolved to prepare a high-concentration flavoring homogenate. Slowly pour this homogenate into the ripened goat milk while stirring at low speed to ensure uniform sweetness and volume distribution, forming a stable basic mixture.

[0043] Step 5: Homogenize The above mixture was placed in a homogenizer and subjected to low-pressure single homogenization at 45°C and 20 MPa. Compared with Example 1, this example uses a lower homogenization pressure to verify the stability under mild shear conditions and the protective effect on lactic acid bacteria activity. After homogenization, the system exhibited a uniform particle size distribution and good flowability.

[0044] Step Six: Freeze-drying Spread the homogenized liquid onto a stainless steel freeze-drying tray, keeping the thickness below 10 mm, and then complete the following freeze-drying process: Quick-freezing stage: Quick-freeze at -50℃ for 6 hours to rapidly form a solid structure and lock in nutrients and bacteria; Low-temperature freeze-drying stage: Freeze-dry at -40℃ and vacuum degree ≤50Pa for 1 hour to initially remove free moisture; Re-temperature freeze-drying stage: Slowly raise the temperature to 0℃, maintain a vacuum of ≤50Pa, and freeze-dry for 4 hours to remove bound water; Room temperature freeze-drying stage: Further increase the temperature to 30°C, keep the vacuum level unchanged, and continue freeze-drying for 12 hours to ensure that the final moisture content is less than 3% and form a loose and porous freeze-dried block.

[0045] Step 7: Crushing and Packaging After freeze-drying, the material is removed and pulverized and sieved under clean conditions, with the sieve mesh controlled at 60-80 mesh. The resulting powder is fine, loose, and has good flowability. It is then immediately packed into aluminum-plastic composite bags, vacuum-sealed, and labeled with the batch number and date before being sealed and stored.

[0046] Product performance and effects The freeze-dried yogurt powder prepared in this embodiment was tested and found to have a total viable count of 4.28 × 10⁻⁶ lactic acid bacteria. 7 The CFU / g values ​​showed that Streptococcus thermophilus and Lactobacillus maintained high activity, and Bifidobacterium also had stable survival ability, indicating that low-pressure homogenization and high-temperature fermentation conditions did not have an adverse effect on the bacterial cells.

[0047] Sensory evaluation showed that the product has a natural color, rich flavor, virtually no goaty smell, a balanced sweet and sour taste, dissolves quickly, and after rehydration, it has a yogurt-like texture and taste, making it widely suitable for the elderly and people with lactose intolerance. It has excellent stability at room temperature and a shelf life of over 12 months.

[0048] This embodiment further verifies the flexibility of the method of the present invention under multiple parameter conditions such as fermentation temperature, post-ripening time, flavoring concentration and homogenization pressure, and confirms its feasibility and reliability for wide industrial application.

[0049] Example 3

[0050] In this embodiment, the effects of different combinations of starter cultures on the activity and flavor of the product's lactic acid bacteria were further investigated. The operating procedure used was basically the same as in Example 1, with only the fermentation strains and addition methods being adjusted.

[0051] Key changes: The starter culture uses only Lactobacillus and Streptococcus thermophilus (excluding Bifidobacterium); The fermentation temperature was set at 41℃, and the fermentation time was 6 hours. The freeze-drying process remains consistent with that of Example 1.

[0052] Result evaluation: After testing, the total viable count of lactic acid bacteria in the product was approximately 2.65 × 10⁻⁶. 7 CFU / g, of which Streptococcus thermophilus was 1.6 × 10⁻⁶. 7 CFU / g, Lactobacillus was 1.05 × 10⁻⁶. 7 CFU / g. Sensory evaluation showed that the flavor was relatively mild, but compared with Example 2, the taste was slightly monotonous and there were fewer types of probiotics.

[0053] Technical Effect Comparison Explanation To verify the impact of different implementation conditions on product performance, the key parameters and test data of Examples 1, 2, and 3 were summarized and analyzed, and the results are shown in the table below:

[0054] Results analysis: Differences in bacterial composition: After introducing Bifidobacterium in Example 2, the total number of viable bacteria and probiotic function remained at a high level, showing that the synergistic fermentation of the three bacterial strains had a significant protective effect on activity. Fermentation and post-ripening optimization: 43℃ high-temperature short-time fermentation combined with a 4℃ post-ripening strategy (Example 2) maintains bacterial activity while achieving moderate acidity and rich flavor; Flavor acceptability: Examples 1 and 2 were superior to Example 3 in sensory scores, indicating that the synergistic use of compound fermentation strains and masking agents is more advantageous for flavor improvement; Adaptability verification: Although Example 3 is a simplified formulation, it still maintains a high bacterial count and good flavor, demonstrating the adjustability and broad applicability of the present invention.

[0055] To further verify the technical effects of this invention compared with existing technologies in terms of lactic acid bacteria survival rate, flavor improvement, and nutrient retention, the following three sets of comparative experiments were conducted: I. Comparative Experiment with Spray Drying Process A yogurt base liquid with the same formula and fermentation conditions as in Example 1 was selected and dried using both the multi-stage freeze-drying method of this invention and the traditional spray-drying method. The number of active lactic acid bacteria was then tested, and the results are as follows:

[0056] The results showed that traditional spray drying resulted in a decrease of approximately 96.5% in the total number of viable bacteria, verifying that the low-temperature multi-stage freeze-drying process of the present invention has significant advantages in the protection of probiotics.

[0057] II. Flavor Effect Experiment of Addition or Absence of α-Cyclodextrin To verify the inhibitory effect of α-cyclodextrin on the muttony odor, the basal fermented goat milk used in Example 1 was divided into two groups: Group A: 0.3% α-cyclodextrin was added according to the method of this invention; Group B: No α-cyclodextrin was added, all other conditions were the same.

[0058] Blind sensory evaluation was conducted after freeze-drying, and the results are as follows:

[0059] Conclusion: The addition of α-cyclodextrin can effectively mask the off-flavor of medium and short-chain fatty acids in goat milk and significantly improve the product's flavor acceptability, which is a key technical improvement measure.

[0060] III. Comparison of the impact of the presence or absence of the "freeze-drying at room temperature" step on live bacteria To verify the effectiveness of "freeze-drying at room temperature" as a non-traditional step, the following control group was set up: Experimental group: The entire process of "rapid freezing - low-temperature freeze-drying - rewarm freeze-drying - room temperature freeze-drying" was adopted; Control group: The "recovery freeze-drying" stage was omitted, and only the three-stage freeze-drying process was performed.

[0061] The viable bacteria count of the freeze-dried product was tested as follows:

[0062] It is evident that the elimination of the warming stage resulted in a decrease of over 33% in the number of viable bacteria, indicating that this step plays a crucial role in the "slow-release warming protection" mechanism of lactic acid bacteria during the warming process, which is not an obvious process in conventional freeze-drying.

[0063] The experimental results above demonstrate that the key technical measures employed in this invention, including the addition of α-cyclodextrin before fermentation, the multi-stage freeze-drying process with a reheating stage, and the differentiated treatment compared to traditional spray drying methods, all produce synergistic and significant technical effects in improving the survival rate of active lactic acid bacteria in freeze-dried yogurt powder, enhancing flavor quality, and extending product shelf life. The various steps work together effectively during implementation, resulting in excellent overall performance in maintaining lactic acid bacteria activity, controlling odor levels, and improving solubility, showcasing the advantages of this invention in the preparation of yogurt powder.

[0064] In summary, this invention, by optimizing the fermentation and freeze-drying process of yogurt goat milk and combining it with a functional flavoring system and flavor-masking agents, successfully produced a freeze-dried yogurt goat milk powder product with high viable bacteria count, good nutrient retention, and significantly enhanced flavor. It is suitable for the elderly and people with special nutritional needs, and has broad market prospects and industrial promotion value, overcoming several technical challenges in existing technologies such as low lactic acid bacteria survival rate, easy nutrient loss, and unsatisfactory flavor.

[0065] It should be noted that the specific embodiments described above are only for illustrating the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that, without departing from the principles and essence of the present invention, several improvements, substitutions or equivalent modifications can be made to the technical solutions of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a freeze-dried acid goat milk powder enriched with lactic acid bacteria, characterized by, Includes the following steps: S1. Dissolving: Mix whole goat milk powder with sterile water at 40℃~50℃ to dissolve it and obtain goat milk liquid; S2. Inoculation with starter culture: Add yogurt starter culture and α-cyclodextrin to the sheep milk and mix well; the yogurt starter culture contains lactobacillus and thermophilic streptococcus. S3. Fermentation: The inoculated sheep milk is fermented at a constant temperature of 41℃~43℃ for 6 to 8 hours, and then matured at 2℃~4℃ for 10 to 12 hours to obtain sour sheep milk. S4. Seasoning premix: Dissolve maltitol solution, isomaltulose and maltodextrin in sterile hot water and prepare a homogenate, then mix it evenly with the sour goat milk; S5. Homogenization: The mixture is homogenized at 40℃~45℃ and 20MPa~25MPa pressure. S6. Freeze-drying: The homogenized material is subjected to quick-freezing, low-temperature freeze-drying, rewarm freeze-drying and room-temperature freeze-drying in sequence to obtain freeze-dried product, which is then crushed and packaged to obtain the freeze-dried yogurt powder. The freeze-drying step includes: (1) Quick-freezing: Quick-freeze at -50℃ for 4 to 6 hours; (2) Low-temperature freeze drying: freeze drying for 1 to 2 hours at -50℃ to -40℃ and vacuum degree ≤50Pa; (3) Re-temperature freeze drying: freeze-dry for 3 to 4 hours under conditions of -30℃ to 0℃ and vacuum degree ≤50Pa; (4) Freeze-drying at room temperature: freeze-dry for 10 to 12 hours at 10℃~30℃ and vacuum degree ≤50Pa.

2. The production method according to claim 1, characterized by, In step S1, the ratio of whole goat milk powder to sterile water is 100g~120g of whole goat milk powder to 1L of sterile water.

3. The preparation method according to claim 1, characterized in that, In step S2, based on the total amount of sheep milk, the amount of yogurt starter added is 0.08%~0.1% (w / v), and the amount of α-cyclodextrin added is 0.1%~0.3% (w / v).

4. The preparation method according to claim 1, characterized in that, In step S4, based on 100 mL of the fermented goat milk, the amount of maltitol solution added is 6.0 g to 8.0 g, the amount of isomaltulose added is 6.0 g to 8.0 g, and the amount of sterile hot water used is 30 mL to 50 mL.

5. The preparation method according to claim 1, characterized in that, In step S3, the constant temperature fermentation temperature is 41℃~43℃, and the fermentation time is 6 hours~8 hours; the post-ripening temperature is 2℃~4℃, and the post-ripening time is 10 hours~12 hours.

6. The preparation method according to claim 1, characterized in that, In step S6, the quick-freezing time is 4 to 6 hours; the low-temperature freeze-drying temperature is -40°C to -50°C; the re-freeze-drying time is 3 to 4 hours; and the room temperature freeze-drying time is 10 to 12 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The yogurt starter also includes Bifidobacteria.

8. A freeze-dried yogurt powder prepared according to any one of claims 1 to 7, characterized in that, The total number of active lactic acid bacteria in the freeze-dried acid goat milk powder is not less than 3.0 x 10 7 CFU / g, including Streptococcus thermophilus and Lactobacillus.

9. The freeze-dried yogurt powder according to claim 8, characterized in that, The viable cell number of the Streptococcus thermophilus is not less than 2.0 x 10 7 CFU / g, and the viable cell number of the Lactobacillus is not less than 1.0 x 10 7 CFU / g.

10. The freeze-dried yogurt powder according to claim 8, characterized in that, The freeze-dried yogurt powder has a shelf life of more than 12 months at room temperature.

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